Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $148.62   3.628%   $154.0119   $154.01   $154.00   $154.00  
  Purchase #2 $175.37   11.216%   $195.0395   $195.04   $195.05   $195.00  
  Purchase #3 $51.35   9.873%   $56.4198   $56.42   $56.40   $56.40  
  Purchase #4 $179.90   7.765%   $193.8692   $193.87   $193.85   $193.90  
  Purchase #5 $137.38   8.822%   $149.4997   $149.50   $149.50   $149.50  
  Purchase #6 $247.97   9.484%   $271.4875   $271.49   $271.50   $271.50  
  Purchase #7 $226.88   7.264%   $243.3606   $243.36   $243.35   $243.40  
  7 purchase totals = $1,167.47       $1,263.6882   $1,263.69   $1,263.65   $1,263.70